+ Xét \(\Delta ABC\) có:
\(\widehat{A}+\widehat{B}+\widehat{C}=180^0\) (định lí tổng 3 góc trong một tam giác).
=> \(30^0+\widehat{B}+\widehat{C}=180^0\)
=> \(\widehat{B}+\widehat{C}=180^0-30^0\)
=> \(\widehat{B}+\widehat{C}=150^0.\)
Mà \(\widehat{B}=2\widehat{C}\left(gt\right)\)
=> \(2\widehat{C}+\widehat{C}=150^0\)
=> \(3\widehat{C}=150^0\)
=> \(\widehat{C}=150^0:3\)
=> \(\widehat{C}=50^0.\)
+ Ta có \(\widehat{B}=2\widehat{C}\left(gt\right)\)
=> \(\widehat{B}=2.50^0\)
=> \(\widehat{B}=100^0.\)
Vậy \(\widehat{B}=100^0;\widehat{C}=50^0.\)
Chúc bạn học tốt!
